A bystander with a Ruger intent on ending the violence almost shot the wrong guy. But he made a split-second decision to keep the weapon in his pocket.

Reporting from Tucson and Washington — Joe Zamudio was out buying cigarettes last Saturday when he heard what sounded like fireworks but quickly realized were gunshots. He reached into his coat pocket for the 9-millimeter semiautomatic pistol he carried, clicking the safety off.

He heard yelling around him: "Shooter, shooter, get down!"

Zamudio saw a young man squirming on the ground and an older man standing above him, waving a gun.

Zamudio, 24, had his finger on the trigger and seconds to decide.

He lifted his finger from the trigger and ran toward the struggling men.

As he grabbed the older man's wrist to wrestle the gun away, bystanders yelled that he had the wrong man — it was the man on the ground who they said had attacked them and U.S. Rep. Gabrielle Giffords (D-Ariz.). The gun the older man was holding had been wrestled away from the shooter. Police later identified 22-year-old Jared Lee Loughner as the suspect.

"I could have very easily done the wrong thing and hurt a lot more people," said Zamudio, who helped subdue the suspect until authorities arrived.

The fact that Zamudio was carrying a gun, and his split-second decision to keep it in his pocket, has come to encapsulate the complexity of the national gun debate.

Gun rights advocates say his quick action showed that a well-armed — and well-trained — person could protect himself and the public.

But gun control advocates see Zamudio's story as an example of how Arizona's gun-friendly culture and lax gun laws have not only failed to make the streets safer, but also have potentially endangered lives.

"They always say, 'What if someone with a concealed weapon was there and could stop this,' " said Kristen Rand, legislative director for the Washington-based Violence Policy Center. "Well there was, and he almost shot the wrong person."

As for Zamudio, he said he was glad he had his gun that day and knows he did the right thing, even if he was not able to stop the shooting.

"I wish I had stopped him sooner," Zamudio said. "We're all responsible to help."

Even if Zamudio hadn't been close by, there was a good chance that someone in the crowd would have been armed. About 40% of Arizona adults own guns, double the percentage in California.

At Black Weapons Armory, a family-owned gun shop in a Tucson strip mall, a small group of staff and customers already knew Zamudio's name and gathered around racks of rifles to discuss the details of the incident.

Phil Davis, a former Marine, nodded as the men around the counter talked about how they were glad they lived in a state where it is legal to carry a gun.

"Arizona has very common-sense gun laws that allow me to protect my family," said Davis, 36, a technology worker, as his two sons fiddled with a rifle scope nearby.

Jeff Prather, a former Green Beret who runs a firearms school at the shop, marveled at Zamudio's composure amid so much confusion. He said most casual gun owners would freeze or focus so tightly on the threat that they would barely notice anything else.

"You think that people could perform like that if they didn't have gun familiarity?" Prather, 53, asked. "That's freedom, and Arizona is leading the way."

Zamudio is definitely ex-military, he figured. Those types of instincts don't come easy.

In fact, Zamudio had no formal firearms training. His father, a prison guard and Vietnam veteran, taught him to shoot as a boy in the desert outside town. When his father died five years ago, he left Zamudio an antique revolver and one rule to live by as a gun owner: "Pray you never have to use it, but be prepared to use it if you have to."

Zamudio, who works at his mother's art gallery, said he has been carrying a gun since he was 19, and prefers to keep it concealed so as not to make people feel uncomfortable. He got a deal last summer on the Ruger P95 he had on him during the shootings.

Looking back, Zamudio sees his years of target practice as preparation for that Saturday morning. With his Ruger in hand, he instinctively ran toward the shooter instead of away.

As he closed in on the two struggling men, he heard the older man with the gun shouting: "I'll kill you!" Still, he resisted the temptation to fire.

It was then that he recognized the Glock 19 in the older man's hand. Zamudio had used that type of weapon before and noticed a key detail: The slide on top of the gun was locked open, indicating it was in the process of being reloaded and wasn't quite ready to use. "I knew he couldn't shoot me," Zamudio said.

Knowing that, he charged forward without shooting. "I decided that I wasn't the one to kill him," he said. "I didn't see the shooting."

He slammed into the older man and held him against a wall until bystanders told him he had the wrong guy.

Then, he and the older man, whose name Zamudio never learned, turned their attention to the younger man, holding him down with the help of two others.